welcome and happy to help. Everyone always thought I was crazy for not cantering for long stretches at a time as i'd build muscle and do trot sets but it makes a HUGE difference. X-training also helps over various terrain for lots of reasons - muscle, bone density, tendon and ligament strength, and so on.
The photos really illustrate for me the changes over the years. When I took that picture of sky at 7, I really thought he looks fantastic and that "was just how he jumped". Now seeing how he is muscled and moves, I know he's 10x stronger but at the same time 10x more responsive and balanced and agile, and he doesn't rush - because he is balanced.
Since we do primarily fox hunting/field hunting/hunter paces now, when jumping a near 4' solid obstacle with depth and height and width and sometimes questionable footing, drops, etc., rushing simply put is NOT an option because it could end disastrously - or worse, in catastrophic injuries to either or both me and my horse.
It took a LOT of discipline and patience to not canter (we didn't canter pretty much the entire first year I had him) and focus in the off season on 99% - 100% trot work. I prefer to canter, it's more fun. I mean really, given the choice who goes, "oh yes, i'd like to do trot sets ad nauseum without any jumping or cantering for the next several months, that sounds like a party!" lol! But it works. And then when you are ready for jumping, do lots of low gymnastics. I personally am a huge fan of 6 x-rails all set as bounces. Talk about rounding the canter and learning to balance, nothing like no strides between fences to make that happen. And keeping them as x-s builds confidence rather than instilling fear in a green horse.
Eventually we've worked up to doing 3'9" - 4'3" bounces. Talk about a challenge! (we stopped that though since my horse HATES that stuff now that we're focused on field hunting where super tight related distances aren't a focus, but jumping clean and technical is) lol